It is known that by adding an inorganic or organic pigment or pigments capable of absorbing light of a specific wavelength range to eyeglass lenses, the anti-glare properties and visibility of such lenses improve.
Protective eyeglasses are used to shield against ultraviolet and visible radiation harmful to the wearer's eyes and to block transmission of light that can cause glare to the eyes.
If it is necessary to strictly avoid radiation that causes glare to the eyes, e.g. for a person who is suffering from retinitis pigmentosa, it is essential to completely cut ultraviolet and visible radiation having wavelengths of 500 nm and shorter.
If it is necessary to reduce glare to the eyes to some extent, e.g. for a person who is suffering from cataract, it is appropriate to use protective eyeglasses that can sufficiently cut radiation having wavelengths of 420 nm and shorter.
In order to keep wearing such protective eyeglasses while walking, anti-glare properties have to be adjusted such that the wearer can tell between the three colors of traffic signals. For this purpose, it is necessary to keep the light transmission at 75% or higher while keeping the ability to sufficiently cut radiation with wavelengths of 420 nm and shorter.
One known medical lens used for such protective sunglasses is a resin lens made mainly of diethylene glycol allyl carbonate, which is also generally known as “CR39”, and containing organic cobalt, and formed by casting polymerization with a polarizing film buried in the resin, the lens having anti-glare properties and polarizing capability (see the below-identified Patent document 1).
A light shielding lens is also known which is dyed by a yellowish disperse dye having an absorption peak wavelength of 390 to 410 nm, a spectral transmittance of 0 to 70% at the absorption peak wavelength, and a molecular absorption coefficient at 20° C. of 2×103 at the absorption peak wavelength (see the below-identified Patent document 2).
Indole-based compounds are known as ultraviolet absorbing agents or anti-halation dyes which can be added to colored resin compositions, resin films, thermal recording materials, liquid crystal display materials, etc (see the below-identified Patent document 3).